Typically such a bending brake has a clamp device that holds the plate or sheet workpiece down on the stationary table with its end projecting forward past the front edge of the table, over the pivotable table which starts in a position underneath the plane of the stationary table. Two arms carry and flank the pivotable table and have inner ends supported on gudgeons or pivots that define for this table a pivot axis that can be adjusted vertically and horizontally according to workpiece size.
Normally the clamp device has a rounded front edge of a predetermined radius of curvature, which eventually becomes the inside radius of curvature of the bend formed in the workpiece. Thus for a given workpiece thickness and bend radius it is necessary to set the height of this pivot axis, that is its spacing above the surface of the stationary table, and then to set the horizontal spacing between this axis and the rear edge of the pivotable table. To this end the gudgeons are carried in vertically displaceable supports and the pivotable table can be shifted radially of its axis along the arms that carry it. The procedure for setting the brake therefore is a cumbersome two-part operation.
In addition it is necessary to provide a suppcrt arrangement permitting the pivot axis to be moved vertically and to mount the pivotable table slidably on its arms. This structure makes the equipment quite expensive, especially as the forces exerted against the pivot are considerable.
Another problem is that in general in such a press it is necessary to design everything so that it is very robust, that is capable of exceeding its nominal rating by a substantial margin without damage to its parts. If this is not done it is possible to destroy, for instance, the bearings carrying the pivotable table and the elements that move the supports for the pivot gudgeons, relatively easily, for instance, by loading an overthick workpiece into the brake. This requires the use of heavy-duty and expensive actuators, drive spindles, and the like, all greatly augmenting the cost of the machine.
It has been suggested to simplify this arrangement somewhat by making the pivot axis stationary and moving the other table that is stationary during the bending operation vertically and horizontally in accordance with workpiece thickness and bending radius. Such an arrangement has certain advantages, but still requires that the adjustment of the equipment entail two independent steps, the vertical and the separate horizontal positioning, the only change being that the pivot axis can remain stationary with the normally stationary table being vertically adjusted.